1. Field of the Invention
The present invention relates to an optical pickup apparatus for reproduction of an information record medium in which information record layers are multiply formed.
2. Description of the Related Art
An optical disk such as a DVD (Digital Video or Versatile Disk) may have such a construction that information record layers are multiply formed so as to improve the record density. At a time of reproducing this type of optical disk, the light beam from the optical pickup is condensed or focused on one of the information record layers of the optical disk, and its reflection light is condensed on a photo detector
However, if the light beam is condensed on one information record layer in the above described manner, the reflection light from another information record layer in a defocus condition is superimposed to the record signal at a time of reproducing one information record layer. This results in a cross talk condition of the record signals. Since there is no correlation between the record signals of these information record layers to each other, there is raised a problem that the signal from another information record layer gives a harmful effect as a random noise onto the quality of the record signal of one information record layer to be reproduced.